Field, Laboratory, and Modeling Studies on the Degradation and

11 Field, Laboratory, and Modeling Studies on the Degradation and Transport of Aldicarb Residues in Soil and Ground Water Russell L. Jones Union Carbide Agricultural Products Company, Inc., Research Triangle Park, NC 27709

Research conducted on the movement and degradation of aldicarb residues in the unsaturated and saturated zones has shown that it is a complex process affected by soil and hydrogeological properties, climatic conditions, and agricultural practices. This paper presents the results of unsaturated and saturated zone field studies conducted in 16 states over a period of six years in which approximately 20,000 soil and water samples have been collected. Results from laboratory degradation studies are also included. Computer modeling has been used to illustrate the effects of variables such as soil field capacity, soil organic matter, pesticide application timing, and climatic conditions on the potential for aldicarb residues to reach groundwater. These experimental and modeling studies show that in most areas aldicarb residues degrade in the upper portion of the unsaturated zone. In the relatively few areas where aldicarb residues reach groundwater, the primarily lateral movement of groundwater and the continuing degradation usually limit the presence of aldicarb residues to shallow groundwater near treated fields. The development o f modem a n a l y t i c a l methodology h a s made p o s s i b l e t h e d e t e c t i o n and q u a n t i f i c a t i o n o f e x t r e m e l y low concentrations o f chemicals. The a p p l i c a t i o n o f t h i s t e c h n o l o g y t o groundwater a n a l y s e s made p o s s i b l e t h e d e t e c t i o n o f t r a c e l e v e l s o f a l d i c a r b r e s i d u e s i n Long I s l a n d groundwater i n 1979 ( 1 ) . This f i n d i n g prompted r e s e a r c h on t h e e n v i r o n m e n t a l f a t e o f w a t e r - s o l u b l e p e s t i c i d e s b y s c i e n t i s t s i n u n i v e r s i t i e s , r e g u l a t o r y a g e n c i e s , and a g r i c u l t u r a l c h e m i c a l m a n u f a c t u r e r s . Much o f t h i s r e s e a r c h f o c u s e d on a l d i c a r b and two o f i t s m e t a b o l i t i e s ( a l d i c a r b s u l f o x i d e and a l d i c a r b s u l f o n e ) . A l t h o u g h much i n d e p e n d e n t r e s e a r c h , e s p e c i a l l y l a b o r a t o r y s t u d i e s , h a s been p e r f o r m e d (samples o f s u c h work a r e i n c l u d e d i n r e f e r e n c e s 2-7), t h i s p a p e r w i l l f o c u s on l a b o r a t o r y and f i e l d r e s e a r c h work i n w h i c h U n i o n C a r b i d e s c i e n t i s t s h a v e p a r t i c i p a t e d o f t e n i n c o o p e r a t i o n w i t h s c i e n t i s t s from u n i v e r s i t i e s or regulatory agencies. 0097-6156/86/0315-0197$06.50/0 © 1986 A m e r i c a n C h e m i c a l Society

198

E V A L U A T I O N O F PESTICIDES IN G R O U N D WATER

Summary o f E x p e r i m e n t a l Methodology U n s a t u r a t e d Zone S t u d i e s . These e x p e r i m e n t s began i n 1980 a t s p e c i a l i n t e r e s t a r e a s i n t h e U n i t e d S t a t e s . I n e a c h a r e a , two t o f i v e l o c a t i o n s , w h i c h were g r o w e r - t r e a t e d f i e l d s , were sampled once or twice a f t e r a p p l i c a t i o n . S o i l c o r e s were t a k e n by hand auger a t t h r e e s i t e s p e r l o c a t i o n w i t h s a m p l i n g o f s t r a t a from 0-0.3, 0.3-0.6, 0.6-1.2, 1.2-1.8, and 1.8-2.4 m. I n 1981, t h e number o f s a m p l i n g i n t e r v a l s a t e a c h l o c a t i o n was i n c r e a s e d t o p r o v i d e a b e t t e r e s t i m a t e o f d e g r a d a t i o n and movement. To r e d u c e t h e e f f e c t s of the i n h e r e n t v a r i a b i l i t y a s s o c i a t e d w i t h f i e l d s t u d i e s , s e v e r a l s a m p l i n g changes were made b e g i n n i n g i n 1982. T e s t f i e l d s were c a r e f u l l y s e l e c t e d i n h i g h use o r p o t e n t i a l use a r e a s . Application was s u p e r v i s e d by u n i v e r s i t y o r company p e r s o n n e l . E a c h t r e a t m e n t was r e p l i c a t e d i n f o u r s u b p l o t s and f o u r c o r e s were t a k e n i n each s u b p l o t by a s p e c i a l b u c k e t auger t e c h n i q u e d e s i g n e d t o r e d u c e c o n t a m i n a t i o n between s o i l s t r a t a . I n a t y p i c a l s t u d y , about 100 s o i l samples would be t a k e n a t a g i v e n s a m p l i n g i n t e r v a l i n each p l o t r e p r e s e n t i n g a s i n g l e treatment. F i e l d s t u d i e s i n c l u d e d from t h r e e t o seven s a m p l i n g i n t e r v a l s a f t e r a p p l i c a t i o n . On t h e a v e r a g e , one a r e a would i n c l u d e two t r e a t m e n t s and y i e l d 800 s o i l samples p e r y e a r t o p r o v i d e s u f f i c i e n t i n f o r m a t i o n f o r e s t i m a t i o n o f d e g r a d a t i o n and movement p a r a m e t e r s . However, i n 1984 a s t u d y was conducted t o a s s e s s t h e e f f e c t o f s p a t i a l v a r i a b i l i t y on measurement of d e g r a d a t i o n and movement. T h i s s t u d y i n v o l v e d 64 c o r e s p e r i n t e r v a l and t h e c o l l e c t i o n and a n a l y s i s o f o v e r 3,100 s o i l samples. S a t u r a t e d Zone S t u d i e s . B e g i n n i n g i n 1983, s a t u r a t e d zone s t u d i e s were c o n d u c t e d u s i n g s e v e r a l c l u s t e r s o f t e s t w e l l s s c r e e n e d a t v a r i o u s depths and l o c a t e d u p g r a d i e n t , w i t h i n , and downgradient o f t h e t r e a t e d a r e a . A minimum o f f i v e c l u s t e r s o f t h r e e w e l l s e a c h i s needed a t any one s t u d y a r e a t o e f f e c t i v e l y a s s e s s movement and d e g r a d a t i o n o f r e s i d u e s i n t h e groundwater. A t one t e s t s i t e i n F l o r i d a , a p p r o x i m a t e l y 160 t e s t w e l l s were i n s t a l l e d and have been sampled on a m o n t h l y b a s i s . Two l i m i t e d s a t u r a t e d zone s t u d i e s have a l s o been p e r f o r m e d by a n a l y z i n g water t a k e n from t h e o u t l e t o f t i l e s draining treated f i e l d s . I n a d d i t i o n t o s a t u r a t e d zone r e s e a r c h s t u d i e s , about 30,000 p o t a b l e w e l l w a t e r samples f r o m 32 s t a t e s have been c o l l e c t e d . A l t h o u g h n o t s p e c i f i c a l l y c o v e r e d by t h i s p a p e r , i n s i g h t s g a i n e d from these a n a l y s e s are i n c l u d e d i n the d i s c u s s i o n s e c t i o n s . L a b o r a t o r y S t u d i e s . A v a r i e t y o f l a b o r a t o r y s t u d i e s have been p e r f o r m e d i n c l u d i n g d e g r a d a t i o n r a t e s t u d i e s w i t h a c t u a l samples f r o m t h e s a t u r a t e d and u n s a t u r a t e d zones, o x i d a t i o n mechanism s t u d i e s , s a t u r a t e d zone d e g r a d a t i o n mechanism s t u d i e s , p o t e n t i a l f o r s u l f o x i d e o r s u l f o n e r e d u c t i o n s t u d i e s , and d i s t i l l e d water hydrolysis studies. The e x p e r i m e n t a l methodology i n t h e s e experiments v a r i e d a c c o r d i n g t o the study o b j e c t i v e s . Degradation D e g r a d a t i o n Pathway. The d e g r a d a t i o n pathway o f a l d i c a r b ( F i g u r e 1) i s t h e same i n p l a n t s , a n i m a l s , and s o i l . First, aldicarb i s oxidized to a l d i c a r b sulfoxide. A p o r t i o n of the a l d i c a r b s u l f o x i d e

11.

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i s f u r t h e r o x i d i z e d t o a l d i c a r b s u l f o n e . Both a l d i c a r b s u l f o x i d e and a l d i c a r b s u l f o n e , b i o l o g i c a l l y a c t i v e carbamates, a r e c o n c u r r e n t l y degraded t o low t o x i c i t y (non-carbamate) compounds. A l t h o u g h r e d u c t i o n o f a l d i c a r b s u l f o x i d e h a s been d e m o n s t r a t e d u n d e r l a b o r a t o r y c o n d i t i o n s ( 8 ) , f i e l d data demonstrate t h a t n e i t h e r t h e s u l f o x i d e n o r t h e s u l f o n e a r e reduced back t o parent a l d i c a r b o r t o s u l f o x i d e i n t h e s a t u r a t e d o r u n s a t u r a t e d zones. I n t h i s paper, t h e term a l d i c a r b r e s i d u e s r e f e r s t o t h e sum o f a l d i c a r b , a l d i c a r b s u l f o x i d e , and a l d i c a r b s u l f o n e . Many f a c t o r s i n f l u e n c e t h e d e g r a d a t i o n o f a l d i c a r b r e s i d u e s t o b i o l o g i c a l l y i n a c t i v e compounds. Some o f t h e more i m p o r t a n t i n c l u d e t e m p e r a t u r e and pH, and t h e p r e s e n c e o f m o i s t u r e and m i c r o b i a l populations. The f o l l o w i n g p a r a g r a p h s d i s c u s s t h e s e i n more d e t a i l f o r d e g r a d a t i o n o c c u r r i n g i n b o t h t h e u n s a t u r a t e d and s a t u r a t e d zones. u n s a t u r a t e d Zone Dégradation. A f t e r a p p l i c a t i o n , s o i l m o i s t u r e r a p i d l y dissolves aldicarb i n the granule. Once i n s o l u t i o n , t h e d e g r a d a t i o n processes b e g i n immediately. The o x i d a t i o n p r o c e s s i s r e l a t i v e l y r a p i d and l i t t l e o r no p a r e n t a l d i c a r b e x i s t s a month after application. The d e g r a d a t i o n o f a l d i c a r b s u l f o x i d e and a l d i c a r b s u l f o n e i s t h e r e s u l t o f b o t h m i c r o b i a l and c h e m i c a l action. E s p e c i a l l y i n a c i d i c s o i l s , m i c r o b i a l degradation i s b e l i e v e d t o be t h e most i m p o r t a n t mechanism i n t h e r o o t zone, o r t h e u p p e r s t r a t a o f t h e u n s a t u r a t e d zone. F a c t o r s w h i c h t e n d t o increase the degradation rate of a l d i c a r b residues include m i c r o b i a l p o p u l a t i o n s , h i g h t e m p e r a t u r e s , h i g h s o i l pH and h i g h s o i l m o i s t u r e content. The d e g r a d a t i o n r a t e o f a l d i c a r b r e s i d u e s i n t h e u n s a t u r a t e d zone h a s been d e t e r m i n e d from f i e l d s t u d i e s conducted s i n c e 1982 i n t e n d i f f e r e n t s t a t e s (9-15) ( T a b l e I ) where h a l f - l i f e ranged between two weeks and t h r e e months. D a t a from t h e s e s i t e s i n d i c a t e t h a t s o i l t e m p e r a t u r e appears t o b e t h e most dominant v a r i a b l e a f f e c t i n g h a l f - l i f e o f a l d i c a r b r e s i d u e s under normal a g r i c u l t u r a l c o n d i t i o n s i n t h e u n s a t u r a t e d zone, w i t h i n c r e a s i n g temperatures r e s u l t i n g i n f a s t e r degradation. Once below t h e r o o t zone, no d e c r e a s e i n t h e d e g r a d a t i o n r a t e w i t h d e p t h was o b s e r v e d e x c e p t i n a c i d i c , sand subsoils. Because o f t h e d e c r e a s e i n m i c r o b i a l p o p u l a t i o n w i t h d e p t h , t h i s r e l a t i v e l y c o n s t a n t d e g r a d a t i o n r a t e as a f u n c t i o n o f d e p t h i n d i c a t e s t h a t s o i l c a t a l y z e d c h e m i c a l h y d r o l y s i s may b e an i m p o r t a n t d e g r a d a t i o n mechanism even i n t h e r o o t zone o f many s o i l s . S a t u r a t e d Zone Dégradâtion. Because o f t h e r a p i d o x i d a t i o n p r o c e s s i n t h e r o o t zone, p a r e n t a l d i c a r b i s r a r e l y d e t e c t e d i n t h e s a t u r a t e d zone. I n r a r e i n s t a n c e s where t r a n s p o r t from t h e s o i l s u r f a c e i s r a p i d , a l d i c a r b may be p r e s e n t a t l e s s t h a n f i v e p e r c e n t o f t h e t o t a l r e s i d u e s found. I n t h e s a t u r a t e d zone, r e s i d u e s a r e u s u a l l y a m i x t u r e o f a l d i c a r b s u l f o x i d e and a l d i c a r b s u l f o n e i n an average r a t i o o f 3:2. I f a l d i c a r b r e s i d u e s l e a c h i n t o t h e s a t u r a t e d zone, o r groundwater, d e g r a d a t i o n o f t h e r e s i d u e s c o n t i n u e s , m a i n l y b y c h e m i c a l h y d r o l y s i s i n c o l d a r e a s and b y b o t h c h e m i c a l h y d r o l y s i s and m i c r o b i a l d e g r a d a t i o n i n warm a r e a s . F a c t o r s which tend t o i n c r e a s e t h e d e g r a d a t i o n r a t e a r e h i g h temperature and h i g h pH. M i c r o b i a l p o p u l a t i o n s may p r o v i d e a s i g n i f i c a n t c o n t r i b u t i o n t o

11.

JONES


201

s a t u r a t e d zone d e g r a d a t i o n , e s p e c i a l l y i n s h a l l o w groundwater i n warm a r e a s . H a l f - l i f e d e g r a d a t i o n r a t e s i n t h e s a t u r a t e d zone, as measured i n t h e l a b o r a t o r y ( T a b l e I I ) , r a n g e f r o m about t h r e e days f o r e a s t c o a s t a l F l o r i d a t o s e v e r a l y e a r s f o r e a s t e r n Long I s l a n d , New Y o r k . I n t h e s e e x p e r i m e n t s , t h e measured d e g r a d a t i o n r a t e s a r e 3 t o 40 t i m e s f a s t e r t h a n would b e p r e d i c t e d on t h e b a s i s o f d i s t i l l e d water h y d r o l y s i s . ( 1 6 ) T h i s i n d i c a t e s t h a t even i n d e e p e r groundwater some c a t a l y t i c f a c t o r s ( m i c r o b e s , m e t a l s , s u r f a c e sorption e f f e c t s ) are present. P r e l i m i n a r y d a t a f r o m an o n g o i n g mechanism s t u d y i n d i c a t e t h a t t h e r a t e i n c r e a s e i s m o s t l y due t o t h e p r e s e n c e o f s o i l r a t h e r t h a n m i c r o b e s . Work b y t h e U n i v e r s i t y o f W i s c o n s i n h a s i n d i c a t e d a h a l f - l i f e o f s i x months t o one y e a r i n W i s c o n s i n groundwater (5-10°C) w h i c h a g r e e s w i t h t e m p e r a t u r e e x t r a p o l a t e d l a b o r a t o r y d a t a u s i n g a c t u a l f i e l d samples. Movement The d r i v i n g f o r c e f o r movement o f a l d i c a r b r e s i d u e s i s t h e movement of water. T h e r e f o r e , t h e movement o f w a t e r must be d e f i n e d b e f o r e t h e movement o f a l d i c a r b r e s i d u e s c a n b e q u a n t i f i e d . F a c t o r s i n f l u e n c i n g t h e movement o f w a t e r i n c l u d e r a i n f a l l , i r r i g a t i o n , évapotranspiration and s o i l f i e l d c a p a c i t y i n t h e u n s a t u r a t e d zone. The amount o f o r g a n i c m a t t e r d e t e r m i n e s t h e r a t e o f a l d i c a r b movement r e l a t i v e t o water movement i n b o t h t h e u n s a t u r a t e d and s a t u r a t e d zones. Movement o f A l d i c a r b f r o m t h e G r a n u l e . A l d i c a r b i s r e l e a s e d from t h e a p p l i e d g r a n u l e s upon c o n t a c t w i t h s o i l m o i s t u r e . I f t h e ground i s e x t r e m e l y d r y , no a l d i c a r b w i l l be r e l e a s e d u n t i l t h e ground i s moistened by r a i n f a l l o r i r r i g a t i o n . In arid climates, i r r i g a t i o n a f t e r a l d i c a r b a p p l i c a t i o n i s recommended. Under most a g r i c u l t u r a l c o n d i t i o n s , a l d i c a r b i s r e l e a s e d from t h e granule w i t h i n hours by normal s o i l moisture. U n s a t u r a t e d Zone Movement. Because a l d i c a r b , a l d i c a r b s u l f o x i d e , and a l d i c a r b s u l f o n e do n o t s i g n i f i c a n t l y b i n d t o i n o r g a n i c s o i l (10,17,18) and a r e s o l u b l e i n w a t e r , a l d i c a r b r e s i d u e s move w i t h s o i l w a t e r i n b o t h t h e u n s a t u r a t e d and s a t u r a t e d z o n e s . Surface s o i l , t h e u p p e r l a y e r o f t h e u n s a t u r a t e d zone, 0.3 t o 1.5 m deep d e p e n d i n g on t h e c r o p , i s o f t e n termed t h e r o o t zone. In the root zone, a l d i c a r b r e s i d u e s move downward w i t h w a t e r f r o m r a i n o r irrigation. Conversely, p l a n t t r a n s p i r a t i o n o f water w i l l tend t o r e t a i n r e s i d u e s i n t h e r o o t zone. E v a p o r a t i o n o f s o i l m o i s t u r e from t h e l a n d s u r f a c e w i l l draw s o i l m o i s t u r e and a l d i c a r b r e s i d u e s f r o m t h e r o o t zone toward t h e s u r f a c e . Movement o f a l d i c a r b r e s i d u e s i n t h e l o w e r s t r a t a o f t h e u n s a t u r a t e d zone i s g e n e r a l l y i n a v e r t i c a l direction. However, s o i l s t r u c t u r e s s u c h as c l a y l e n s e s o r hardpans may r e s u l t i n some h o r i z o n t a l movement. A l d i c a r b r e s i d u e s do s o r b t o o r g a n i c m a t t e r and i n some h i g h o r g a n i c m a t t e r s o i l s t h e r a t e o f r e s i d u e movement may be up t o a f a c t o r o f t e n s l o w e r t h a n t h e r a t e o f w a t e r movement. F a c t o r s w h i c h i n c r e a s e downward movement a r e a h i g h r e c h a r g e r a t e ( r a i n f a l l p l u s i r r i g a t i o n minus é v a p o t r a n s p i r a t i o n ) , low s o i l f i e l d c a p a c i t y , and low s o i l o r g a n i c matter. I n many c a s e s , movement i n t h e u n s a t u r a t e d zone i s t h e r e s u l t o f a few r e l a t i v e l y heavy r a i n s .


202

Table I .

A l d i c a r b and A l d i c a r b S u l f o n e

Crop Arizona 1982 M a r i c o p a Aldicarb Aldicarb Aldicarb Aldicarb

a t Emergence a t P l a n t i n g and Emergence Sulfone at Planting S u l f o n e a t Emergence

Cotton

California 1980 E x p l o r a t o r y S t u d i e s a t Two S i t e s ( A l d i c a r b ) 1984 Manteca ( A l d i c a r b ) Livingston (Aldicarb) Fresno ( A l d i c a r b )

Cotton Tomatoes Grapes Grapes

Colorado 1984 E x p l o r a t o r y S t u d i e s a t Three S i t e s ( A l d i c a r b )

Potatoes

Florida 1980 1981 1982 1983

Exploratory Studies at Five S i t e s (Aldicarb) Exploratory Studies at Five S i t e s (Aldicarb) Indlantown ( A l d i c a r b ) Lake H a m i l t o n ( A l d i c a r b ) Ovledo ( A l d i c a r b ) Alcoma ( A l d i c a r b ) Indlantown ( A l d i c a r b ) Lutz ( A l d i c a r b ) Lake Buena V i s t a ( A l d i c a r b ) DeLeon S p r i n g s ( A l d i c a r b ) Fort Pierce (Aldicarb) 1984 Oavenport ( A l d i c a r b ) Lake Hamilton ( A l d i c a r b Alcoma ( A l d i c a r b ) Lutz ( A l d i c a r b ) DeLeon S p r i n g s ( A l d i c a r b ) Monitoring Wells ( A l d i c a r b ) 1985 Lake H a m i l t o n ( A l d i c a r b ) Lutz ( A l d i c a r b ) DeLeon S p r i n g s ( A l d i c a r b ) Monitoring Wells ( A l d i c a r b )

Citrus

Tomatoes Citrus

•Average c o n c e n t r a t i o n 1n s o i l c o r e s o r water samples

11.

JONES


F i e l d Research Programs - 1 9 8 0 - J u l y , 1985. No. of Samples Soi 1 Water

1176

28 584 351 759

40

141 445 575 354

224 3127

4 247

3

23 88 31 298 171 146 91 55 18 50 20 1187 212 49 29 44 820 12 13 73

A p p l i c a t i o n Rate kg/ha

Unsaturated Zone Half-Life (months)

2.24 1.12,2.24 3.36 2.24

0.5 0.3, 0.5 0.3

0.61-2.5 3.36 4.48 4.48

1.5 1.5 1.5

Maximum Leaching Depth (m)*

1.8 1.8 1.8 1.8

0.8

1.2 1.8 1.2 3.0

1.2

3.36

5.6-11.2 5.6-11.2 7.56 11.2 11.2

—

2.4 2.4

0.6 0.6

3.0 1.2

7.56

-3.36 5.6

—

0.6 6.0

5.6 — __

5.6

1s l e s s than 5 ppb below t h i s d e p t h . Continued

on next page


Table I .


Crop Indiana Corn

1983 B l u e c a s t ( A l d i c a r b ) Maine

Potatoes

1983 Presque I s l e ( A l d i c a r b ) Planting Application Emergence A p p l i c a t i o n Michigan 1983 B l 1 s s f 1 e l d

Corn

(Aldicarb)

Nebraska 1985 B a r t l e t t

Corn

(Aldicarb)

New York Potatoes

1983 Phelps ( A l d i c a r b ) Planting Application Emergence A p p l i c a t i o n North C a r o l i n a 1983 H a r r e l l s v l l l e Aldicarb at Transplanting A l d i c a r b Sulfone at Transplanting

Tobacco

Oregon 1980 E x p l o r a t o r y

S t u d i e s a t One S i t e

(Aldicarb)

Potatoes

South C a r o l i n a 1985 E d l s t o

Soybeans Bare P l o t

(Aldicarb)

Texas 1980 E x p l o r a t o r y

S t u d i e s a t Three S i t e s

(Aldicarb)

Citrus

•Average c o n c e n t r a t i o n 1n s o i l c o r e s or water

11.

JONES


F i e l d Research Programs - 1 9 8 0 - J u l y ,

No. of Samples Soil Water

208

20

1440


U n s a t u r a t e d Zone Half-Life Maximum Leaching (months) Depth ( m ) *

1.1

0.6

3.36 2.24

3.3 2.8

1.5 1.2

0.7

0.6

3.36 2.24

1.0 0.9

0.3 0.3

3.36 3.36

1.3 0.9

0.6 0.6

3.36

—

1.2

-

1.8

16

1.68

111

51

1.7

656

(continued).

1.68

192

456

1985

205

15

1

135 136

143

3.4 3.4

41

7

5.6

samples 1s l e s s than 5 ppb below t h i s d e p t h . Continued

on next page


Table ! •


Field

Crop Virginia 1980 E x p l o r a t o r y S t u d i e s a t Two S i t e s ( A l d i c a r b ) 1981 E x p l o r a t o r y S t u d i e s a t Three S i t e s ( A l d i c a r b ) 1983 B l a c k s t o n e Aldicarb at Transplanting A l d i c a r b Sulfone at Transplanting

Potatoes Potatoes Tobacco

Washington 1980 E x p l o r a t o r y S t u d i e s a t Two S i t e s ( A l d i c a r b ) 1983 Pasco ( A l d i c a r b )

Potatoes

Wisconsin 1980 E x p l o r a t o r y S t u d i e s a t F i v e S i t e s ( A l d i c a r b ) Potatoes 1981 E x p l o r a t o r y S t u d i e s a t S i x S i t e s ( A l d i c a r b ) 1982 Hancock ( A l d i c a r b ) Emergence A p p l i c a t i o n w i t h Moderate I r r i g a t i o n P l a n t i n g A p p l i c a t i o n w i t h Moderate I r r i g a t i o n Emergence A p p l i c a t i o n w i t h Heavy I r r i g a t i o n P l a n t i n g A p p l i c a t i o n w i t h Heavy I r r i g a t i o n Cameron ( A l d i c a r b ) Emergence A p p l i c a t i o n Planting Application 1983 Hancock A l d i c a r b a t Emergence Aldicarb at Planting A l d i c a r b Sulfone at Planting

•Average

c o n c e n t r a t i o n 1n s o i l c o r e s or water samples

11.

JONES


207

Research Programs 1980 - J u l y , 1985

No. of Samples Soi 1 Water

39 118

3 27


U n s a t u r a t e d Zone Half-Life Maximum L e a c h i n g (months) Depth ( m ) *

3.36 3.36

—

1.2

3.36 3.36

1.1 1.3

0.6 0.6

3.36 6.72

— 1.7

0.6 1.8

3.36 3.36

—

2.4 2.4

664

24 448

5

127 505 1230

31 65 10

338 1094

21

2.24 3.36 2.24 3.36

1.2 1.7

1.8 2.4 1.8 3.0

2.24 3.36

1.5 2.0

1.2 1.2

2.24 3.36 3.36

1.3 0.9 1.1

1.8 0.6 2.4

1s l e s s than 5 ppb below t h i s d e p t h .


208

TABLE I I .

R e s u l t s of Laboratory Studies Measuring Rates of A l d i c a r b Residues

Sample Location

New Y o r k Long I s l a n d

Compounds Studied

Sulfoxide Sulfone

Approximate pH o f Sample

&

6

Degradation

i n S a t u r a t e d Zone Samples

Study Temp.°C

Calculated HalfL i f e i n Days 1

2

13 25

800 360(243-704)

2

Wisconsin Sulfoxide & C e n t r a l Sands S u l f o n e Sulfone only

7

25

14

( 12,16)

7

25

13

( 10,16)

North C a r o l i n a Sulfoxide & Coastal P l a i n Sulfone Sulfone only

5

25

137(117,165)

5

25

108(63,368)

Florida Lutz

6

25

49

(41,61)

6

25

47

(40,55)

6

25

49

(38,63)

7

25

3

7

25

52

7

25

8

(7-10)

8

25

23

(17,35)

Sulfoxide & Sulfone Lake H a m i l t o n S u l f o x i d e & Sulfone Alcoma Sulfoxide & Sulfone Oveido Sulfoxide & Sulfone Fort Pierce Sulfone only

California Livingston

Sulfoxide & Sulfone

Colorado Sulfoxide & San L u i s V a l l e y S u l f o n e

(1)

Numbers i n p a r e n t h e s i s

are the

(2)

V a r i a t i o n i n l a t e r sampling difficult.

95% c o n f i d e n c e

2

2

(1,5) (40,74)

limits.

i n t e r v a l s makes e s t i m a t i o n o f t h e s e

values

11.

JONES


209

The amount, i f any, o f a l d i c a r b r e s i d u e s l e a c h i n g t o a s p e c i f i e d d e p t h depends b o t h on t h e r a t e o f d e g r a d a t i o n and movement. F o r example, t h e same amount o f l e a c h i n g c o u l d o c c u r i n a s i t u a t i o n where t h e d e g r a d a t i o n r a t e and t h e r a t e o f movement a r e r e l a t i v e l y slow, as i n a s i t u a t i o n where b o t h r a t e s a r e r e l a t i v e l y r a p i d . As discussed e a r l i e r , the rate of degradation of aldicarb residues i n t h e u n s a t u r a t e d zone i s r e l a t i v e l y f a s t ( h a l f - l i f e o f 0.5 t o 3 months). T h e r e f o r e , l e a c h i n g o f r e s i d u e s t h r o u g h t h e u n s a t u r a t e d zone t o groundwater o c c u r s o n l y o c c a s i o n a l l y and t h e n o n l y i n a r e a s w i t h r e l a t i v e l y s h a l l o w w a t e r t a b l e s (where t r a n s p o r t t o t h e water t a b l e may b e a c c o m p l i s h e d q u i c k l y ) o r i n a r e a s w i t h a c i d i c sand s u b s o i l s where d e g r a d a t i o n r a t e s a r e s l o w e r ( s u c h as p o r t i o n s o f Long I s l a n d o r c e n t r a l F l o r i d a w i t h r e l a t i v e l y deep w a t e r t a b l e s ) . The d e p t h t o w h i c h d e t e c t a b l e l e a c h i n g o f a l d i c a r b r e s i d u e s o c c u r r e d i n f i e l d s t u d i e s i s l i s t e d i n T a b l e I . L e a c h i n g beyond t h r e e meters o c c u r r e d i n t h e r i d g e a r e a o f F l o r i d a ( s p e c i f i c a l l y Lake H a m i l t o n , Alcoma, D a v e n p o r t ) and w i t h p l a n t i n g a p p l i c a t i o n s i n t h e C e n t r a l Sands o f W i s c o n s i n (Hancock). O t h e r work h a s shown l e a c h i n g below t h r e e meters on Long I s l a n d . (16.19) The d e p t h t o w h i c h a l d i c a r b r e s i d u e s may l e a c h i n a g i v e n s i t e may v a r y from y e a r t o y e a r depending on t h e amount and d i s t r i b u t i o n o f r a i n f a l l and irrigation. The t i m i n g o f an a p p l i c a t i o n r e l a t i v e t o weather ( r a i n f a l l and s o i l t e m p e r a t u r e ) may a f f e c t b o t h t h e r a t e o f movement and t h e d e g r a d a t i o n r a t e , as d e m o n s t r a t e d i n W i s c o n s i n ( 9 ) , F l o r i d a ( 2 0 ) , and t h e n o r t h e a s t e r n U n i t e d S t a t e s (11.12). S a t u r a t e d Zone Movement. The movement o f a l d i c a r b r e s i d u e s i n t h e s a t u r a t e d zone i s i n t h e same d i r e c t i o n as groundwater movement. I n most a r e a s , t h i s means t h a t i f a l d i c a r b r e s i d u e s r e a c h t h e s a t u r a t e d zone, t h e y w i l l move p r i m a r i l y i n a h o r i z o n t a l d i r e c t i o n . Since t h e r e i s u s u a l l y l i t t l e o r g a n i c m a t t e r i n t h e s a t u r a t e d zone, a l d i c a r b r e s i d u e s t r a v e l a t t h e same speed as t h e groundwater, g e n e r a l l y 0.03 t o 0.5 m p e r day. The r e s i d u e s t e n d t o r e m a i n n e a r t h e t o p o f t h e s a t u r a t e d zone and v e r t i c a l movement i s slow. I n o n l y a few a r e a s where a l d i c a r b i s u s e d have r e s i d u e s a c t u a l l y been found t o move t h r o u g h t h e u n s a t u r a t e d zone b e f o r e b e i n g c o m p l e t e l y degraded. I n these areas, the p o t e n t i a l f o r p r e s e n c e o f r e s i d u e s i n d r i n k i n g water w e l l s depends on t h e amount o f r e s i d u e s e n t e r i n g groundwater, t h e d e g r a d a t i o n r a t e i n groundwater, t h e r a t e o f groundwater movement and t h e l o c a t i o n , c a s i n g d e p t h and i n t e g r i t y o f d r i n k i n g w a t e r w e l l s n e a r t r e a t e d fields. I n most a r e a s , c o n t i n u e d d e g r a d a t i o n i n t h e s a t u r a t e d zone and t h e slow h o r i z o n t a l movement accompanied by d i s p e r s i o n t e n d t o r e s u l t i n a l d i c a r b r e s i d u e s b e i n g c o n s t r a i n e d t o s h a l l o w groundwater near t r e a t e d areas. Model S i m u l a t i o n U n s a t u r a t e d Zone M o d e l s . V a r i o u s models e x i s t f o r e s t i m a t i n g t h e movement and d e g r a d a t i o n o f p e s t i c i d e r e s i d u e s i n t h e u n s a t u r a t e d zone ( 2 0 ) . Perhaps t h e b e s t model a v a i l a b l e i s PRZM d e v e l o p e d b y t h e U.S. EPA ( 2 1 ) . The a p p l i c a b i l i t y o f PRZM t o t h e m o d e l i n g o f a l d i c a r b r e s i d u e s h a s been d e m o n s t r a t e d u s i n g d a t a from Long I s l a n d ( 2 2 ) , F l o r i d a ( 2 0 ) , W i s c o n s i n (23.23.24). and N o r t h C a r o l i n a (24)·

210


One o f t h e most i m p o r t a n t u s e s o f an u n s a t u r a t e d zone model i s to i l l u s t r a t e the e f f e c t s of v a r i a b l e s . I n F i g u r e 2, PRZM has been used to i l l u s t r a t e the e f f e c t of o r g a n i c matter, s o i l h y d r a u l i c p r o p e r t i e s , and d e g r a d a t i o n r a t e on t h e amount o f l e a c h i n g . The i n p u t p a r a m e t e r s l i s t e d i n T a b l e I I I have been used as a b a s i s f o r t h e s e s i m u l a t i o n s . The e n v i r o n m e n t a l c o n d i t i o n s o f t h i s example a r e s i m i l a r t o t h o s e o f t h e r i d g e c i t r u s growing a r e a i n c e n t r a l Florida. The b a s e c a s e i l l u s t r a t i o n chosen was one where p o t e n t i a l f o r movement t o t h e water t a b l e i s h i g h . Downward movement i s r a p i d due t o h i g h r a i n f a l l , e x t r e m e l y low f i e l d c a p a c i t y f o r t h e s o i l , and low s o r p t i o n t o s o i l . As F i g u r e 2 shows, even s m a l l changes i n percent organic matter or f i e l d c a p a c i t y w i l l s i g n i f i c a n t l y a f f e c t t h e d i s t a n c e r e s i d u e s move b e f o r e b e i n g decomposed. S m a l l changes i n d e g r a d a t i o n r a t e have a s i g n i f i c a n t impact as w e l l . These t y p e s o f s i m u l a t i o n s h e l p e x p l a i n t h e d i f f e r e n c e s seen i n F l o r i d a f i e l d s t u d i e s i n t h e magnitude o f r e s i d u e s found i n s h a l l o w groundwater u n d e r t r e a t e d c i t r u s g r o v e s i n c o a s t a l and r i d g e a r e a s . The h i g h e r s o i l f i e l d c a p a c i t y and h i g h e r o r g a n i c m a t t e r c o n t e n t t y p i c a l o f e a s t e r n c o a s t a l a r e a s r e s u l t s i n much lower r e s i d u e s e n t e r i n g s h a l l o w groundwater compared t o t h e r i d g e a r e a . S i m u l a t i o n s u s i n g t h e a c t u a l p a r a m e t e r s f o r c o a s t a l c i t r u s (and other southeastern l o c a t i o n s ) coupled with experimental data confirm t h a t t h e c e n t r a l F l o r i d a r i d g e a r e a i s more s e n s i t i v e t o l e a c h i n g o f a l d i c a r b r e s i d u e s t o groundwater compared t o o t h e r s o u t h e a s t e r n a g r i c u l t u r a l areas. Because b o t h t h e amount and d i s t r i b u t i o n o f r a i n f a l l and évapotranspiration change from y e a r t o y e a r a t a s p e c i f i c s i t e , m o d e l i n g can h e l p g e n e r a l i z e e x p e r i m e n t a l r e s u l t s . One method f o r i l l u s t r a t i n g t h e e f f e c t o f y e a r - t o - y e a r weather v a r i a t i o n s i s t o perform a s i m u l a t i o n with s e v e r a l consecutive years of r a i n f a l l . The r e s u l t s o f t h i s s i m u l a t i o n can t h e n be summarized i n a cumulative p r o b a b i l i t y d i s t r i b u t i o n curve. The r e s u l t s o f a 1 7 - y e a r s i m u l a t i o n (1965-1982 w i t h 1978 e x c l u d e d b e c a u s e o f m i s s i n g weather d a t a ) f o r t h e Lake H a m i l t o n , F l o r i d a , l o c a t i o n u s i n g t h e i n p u t p a r a m e t e r s i n T a b l e I I I a r e shown i n F i g u r e 3. This figure shows t h a t 50 p e r c e n t o f t h e t i m e t h e amount o f a l d i c a r b r e s i d u e s l e a c h i n g b e l o w 450 cm i s l e s s t h a n 7 p e r c e n t o f t h a t a p p l i e d when t h e a p p l i c a t i o n d a t e was F e b r u a r y 15. When t h e a p l i c a t i o n d a t a was June 15, 30 p e r c e n t o f t h e a p p l i e d r e s i d u e s l e a c h e d below 450 cm. These d i f f e r e n c e s a r e a r e s u l t o f t h e uneven d i s t r i b u t i o n o f r a i n f a l l during the year. T h e r e f o r e , an a p p l i c a t i o n on F e b r u a r y 15 ( d u r i n g t h e l e s s r a i n y p o r t i o n o f t h e y e a r ) w i l l , on t h e a v e r a g e , r e s u l t i n l e s s r e s i d u e l e a c h i n g below a s p e c i f i e d d e p t h , t h a n a June 15 a p p l i c a t i o n ( d u r i n g t h e r a i n y p o r t i o n o f t h e y e a r ) . S a t u r a t e d Zone Models. R e s u l t s from u n s a t u r a t e d zone s i m u l a t i o n s can be used as i n p u t s t o s a t u r a t e d zone models t o p r e d i c t c o n c e n t r a t i o n s o f a l d i c a r b r e s i d u e s i n groundwater. The s a t u r a t e d zone model u s e d by t h e a u t h o r t a k e s t h e p e s t i c i d e i n p u t s i n t o groundwater, as p r e d i c t e d by PRZM, and c a l c u l a t e s t h e c o n c e n t r a t i o n and movement o f a l d i c a r b r e s i d u e s i n t h e u p p e r p o r t i o n o f t h e s a t u r a t e d zone. The c o r e o f t h e s a t u r a t e d zone model i s a f i n i t e element s o l u t e t r a n s p o r t c a l c u l a t i o n p r o c e d u r e d e v e l o p e d a t t h e U n i v e r s i t y o f W i s c o n s i n ( 2 5 ) . The a c c u r a c y o f t h i s model i n e s t i m a t i n g p e s t i c i d e movement i n groundwater i s (as w i t h o t h e r

JONES


F i g u r e 2(A,B). S i m u l a t e d e f f e c t o f o r g a n i c m a t t e r (A) and s o i l h y d r a u l i c p r o p e r t i e s (B) on t h e l e a c h i n g o f a l d i c a r b r e s i d u e s under F l o r i d a Ridge c o n d i t i o n s . C o n t i n u e d on n e x t page.

E V A L U A T I O N O F P E S T I C I D E S IN G R O U N D WATER

15 - 30 DAYS HALF LIFE A°_ J ^ Y S HALF LIFE 60 - 120 DAYS HALF LIFE

150

300

450

DEPTH IN CM F i g u r e 2 ( C ) . S i m u l a t e d e f f e c t o f d e h y d r a t i o n r a t e on the l e a c h i n g o f a l d i c a r b r e s i d u e s under F l o r i d a Ridge c o n d i t i o n s .

11.

JONES

213


TABLE I I I .

PRZM Base Case U s i n g F l o r i d a R i d g e C o n d i t i o n s

D a i l y R a i n f a l l Data:

1983 Lake A l f r e d

D a i l y E v a p o r a t i o n Data:

1983 Lake A l f r e d S t a t i o n (Pan F a c t o r o f 1.0)

S o i l Hydraulic

Properties: Field (vol.

S o i l S t r a t a (cm) 0-15 15-30 30-45 45-60 60-75 75-90 90-450 47,

Root Zone Depth (cm):

150

P e s t i c i d e D e g r a d a t i o n Rate ( h a l f l i f e

Uptake o f P e s t i c i d e :

Pesticide

Application:

1.8 1.3 1.2 0.9 0.9 0.6 0.8

67, 83, 59, 77, 89, 40, 60,78

i n days):

Coefficient:

0-15 cm 15-30 cm 30-60 cm Below 60 cm Plant

Wilting Point (vol. percent)

30 30-60 ( i n t e r p o l a t e w i t h depth) 60

0-150 cm 150-300 cm Below 300 cm S o i l Sorption

Capacity percent)

6.7 5.3 6.6 4.3 4.9 4.1 3.8

SCS Curve Numbers:

Pesticide

Station

0.08 0.08 0.03 0.00 Not

considered

11.21 kg/ha on F e b r u a r y 16, 1983

214

E V A L U A T I O N O F P E S T I C I D E S IN G R O U N D WATER

F i g u r e 3. S i m u l a t e d c u m u l a t i v e p r o b a b i l i t y d i s t r i b u t i o n s showing the e f f e c t o f weather (as a f u n c t i o n on depth) and a p p l i c a t i o n t i m i n g on the l e a c h i n g o f a l d i c a r b r e s i d u e s .

11.

JONES

Degradation and

Transport of Aldicarb Residues

215

s a t u r a t e d zone models) l a r g e l y dependent on t h e a c c u r a c y o f t h e input parameters. A s i m p l i f i e d example i s p r e s e n t e d i n F i g u r e 4 w h i c h h e l p s i l l u s t r a t e how a s a t u r a t e d zone model c a n be u s e d i n s i m u l a t i n g a l d i c a r b r e s i d u e c o n c e n t r a t i o n s . T h i s c a s e assumes a s t a r t i n g c o n c e n t r a t i o n o f 100 ppb i n groundwater u n d e r a t r e a t e d a r e a , a groundwater f l o w r a t e o f 0.15 m/day, and a d e g r a d a t i o n r a t e c o r r e s p o n d i n g t o a h a l f - l i f e o f s i x months. These c o n d i t i o n s a r e s i m i l a r t o t h o s e e n c o u n t e r e d i n much o f t h e r i d g e a r e a o f F l o r i d a . Under t h e s e c o n d i t i o n s , 18 months l a t e r , a l d i c a r b r e s i d u e s w i l l be p r e s e n t up t o 82 m downstream o f t h e t r e a t e d a r e a a t a c o n c e n t r a t i o n o f about 12 ppb. The r e s u l t s o f t h e s e model s i m u l a t i o n p r o j e c t i o n s a r e c o n s i s t e n t w i t h r e s u l t s o b t a i n e d from f i e l d e x p e r i m e n t a l s t u d i e s n o t o n l y i n F l o r i d a , but at other l o c a t i o n s . F o r example, i n t h e F l o r i d a r i d g e c i t r u s r e g i o n , a l d i c a r b r e s i d u e s have n o t been d e t e c t e d i n s h a l l o w groundwater a t d i s t a n c e s o f more t h a n 200-300 m downgradient o f t r e a t e d groves. Experimental r e s u l t s a l s o demonstrate t h a t under these c o n d i t i o n s , the a l d i c a r b r e s i d u e s are c o n s t r a i n e d t o the upper 3-6 m o f groundwater due t o d e g r a d a t i o n and l a t e r a l groundwater flow. I n the c o a s t a l r e g i o n s of F l o r i d a , a l d i c a r b r e s i d u e s are c o n s t r a i n e d t o t h e s h a l l o w groundwater w i t h i n t h e p e r i m e t e r o f t h e t r e a t e d f i e l d s o r g r o v e s due t o t h e more r a p i d r a t e o f degradation.(10,26) The r e s u l t s o f t h e s e e x p e r i m e n t a l and model s i m u l a t i o n s t u d i e s h e l p e d p r o v i d e a b a s i s f o r s t a t e r e g u l a t i o n s on the use of a l d i c a r b i n F l o r i d a . Conclusions The e n v i r o n m e n t a l d a t a b a s e f o r a l d i c a r b i s q u i t e e x t e n s i v e , c o n s i s t i n g o f about 20,000 s o i l and w a t e r samples from 38 r e s e a r c h s t u d i e s and 30,000 p o t a b l e w e l l a n a l y s e s . These d a t a i n d i c a t e t h a t a l d i c a r b r e s i d u e s degrade i n b o t h t h e u n s a t u r a t e d and s a t u r a t e d zones w i t h t h e r a t e dependent on a v a r i e t y o f e n v i r o n m e n t a l parameters. I n t h e u n s a t u r a t e d zone, t h e d e g r a d a t i o n r a t e c o r r e s p o n d s t o a h a l f - l i f e o f about two weeks t o t h r e e months w i t h the slower degradation r a t e s o c c u r r i n g i n c o l d e r areas. The d e g r a d a t i o n r a t e i n t h e s a t u r a t e d zone c o r r e s p o n d s t o h a l f - l i v e s r a n g i n g from a few days t o a few y e a r s . D e g r a d a t i o n r a t e s a r e most r a p i d i n warm, a l k a l i n e groundwater. The movement o f a l d i c a r b r e s i d u e s i s q u i t e complex, d e p e n d i n g on a number o f i n t e r a c t i n g f a c t o r s . I n most a l d i c a r b u s e a r e a s , r e s i d u e s degrade c o m p l e t e l y b e f o r e moving t h r o u g h t h e u n s a t u r a t e d zone and i n t o t h e s a t u r a t e d zone. I n t h e few a r e a s where a l d i c a r b r e s i d u e s have e n t e r e d t h e s a t u r a t e d zone, r e s i d u e s a r e u s u a l l y l o c a t e d i n s h a l l o w groundwater n e a r t r e a t e d f i e l d s . When r e q u i r e d i n p u t p a r a m e t e r s a r e a v a i l a b l e , u n s a t u r a t e d and s a t u r a t e d zone models a r e good t o o l s f o r i l l u s t r a t i n g t h e e f f e c t s o f v a r i o u s combinations of v a r i a b l e s , a p p l y i n g experimental data t o f i e l d s i t u a t i o n s , s e l e c t i n g p o t e n t i a l worst case s i t u a t i o n s f o r f u r t h e r assessment, and d e t e r m i n i n g t h e e f f e c t o f management p r a c t i c e s ( s u c h as changes i n a p p l i c a t i o n t i m i n g ) on r e s i d u e movement. The a p p l i c a b i l i t y o f t h e u n s a t u r a t e d zone model t o s i t u a t i o n s i n v o l v i n g a l d i c a r b has been d e m o n s t r a t e d o v e r a wide


216

OJjme _

Q_

6 Months 12 Months 18 Months

25-r

12.5 Treated Area

F i g u r e 4. I l l u s t r a t i o n ridge conditions.

Distance From Treated Area (m)

of saturated

zone m o d e l i n g under F l o r i d a

11.

JONES


217

range o f c o n d i t i o n s and t h e a c c u r a c y o f b o t h u n s a t u r a t e d and s a t u r a t e d zone models p r e d i c t i o n s i s enhanced by t h e a v a i l a b i l i t y o f e x t e n s i v e d a t a on s o r p t i o n and d e g r a d a t i o n r a t e s . Acknowledgments Many s c i e n t i s t s f r o m u n i v e r s i t i e s and r e g u l a t o r y a g e n c i e s have c o n t r i b u t e d t o r e s e a r c h programs t h a t have been d e s c r i b e d i n t h i s paper. I would l i k e t o s p e c i f i c a l l y acknowledge t h e c o n t r i b u t i o n s of: Μ . P. Anderson, R. F. C a r s e l , K. S. P o r t e r , P. S. C. Rao, J . A. Wyman, D. Curwin, J . M. H a r k i n , G. C h e s t e r s , A. G. H o m s b y , W. B. Wheeler, P. N k e d i - K i z z a , J . McNeal, R. J . Wagenet, H. B. Hughes, R. V. Rourke, E. N. L i g h t f o o t , P. S. T h o m e , A. P. Lemley, D. A. Komm, D. P o w e l l , R. 0. Hegg, and P. S t o f f e l a . I would a l s o l i k e t o acknowledge t h e work o f t h e many p e o p l e a t U n i o n C a r b i d e who p a r t i c i p a t e d i n these s t u d i e s . References

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

11. 12.

Zaki, M. H., D. Moran, D. Harris, Am. J. Public Health 1982, 72, 1391-1395. Smelt, J. Η., M. Leistra, W. H. Houx, A. Dekker, Pestic. Sci. 1982, 13, 475-483. Nicholls, P. H., R. H. Bromilow, T. M. Addiscott, Pestic. Sci. 1982, 13, 475-483. Pacenka, S., K. S. Porter, "Preliminary Assessment of the Environmental Fate of Potato Pesticide, Aldicarb, in Soil and Ground Water" Eastern Long Island, New York, U.S. EPA Contract 8006876-02. Lemley, A. J., W. Z. Zhong, J. Environ. Sci. Health 1983, Β 18 (2), 189-206. Rothschild, E. R., R. J. Manser, M. P. Anderson, Ground Water 1982, 20, 437-445. Dierberg, F. Ε., "Aldicarb Studies in Groundwaters from Citrus Groves in Indian River County, Florida," Florida Water Resources Research Center Publication No. 76, 1984. Miles, C. J., J. J. Delfino, J. Agric. Food Chem.. 1985, 33, 455-460. Wyman, J. Α., J. O. Jensen, D. Curwen, R. L. Jones, T. E. Marquardt, "Effects of Application Procedures and Irrigation on Degradation and Movement of Aldicarb Residues in Soil." Accepted for publication, 1985. Hornsby, A. G., P.S. C. Rao, W., B. Wheeler, P. Nkedi-Kizza, R. L. Jones, "Fate of Aldicarb in Florida Citrus Soils: 1. Field and Laboratory Studies," presented at Characterization and Monitoring of the Vadose (Unsaturated) Zone, Las Vegas, December 8-10, 1983. Jones, R. L., R. V. Rourke, J. L. Hansen, "Effect of Application Methods on Movement and Degradation of Aldicarb Residues in Maine Potato Fields." Accepted for publication, 1985. Wagenet, R. J., K. S. Porter, R. L. Jones, T. E. Marquardt, "Aldicarb Movement in the Field Soil of Upstate New York." Submitted for publication, 1985.

218


13. Wyman, J. Α., J. Medina, D. Curwen, J. L. Hansen, R. L. Jones, "Movement of Aldicarb and Aldoxycarb Residues in Soil." Submitted for publication, 1985. 14. Jones, R. L., J. L. Hansen, R. R. Romine, T. E. Marquardt, "Unsaturated Zone Studies on the Degradation and Movement of Aldicarb and Aldoxycarb Residues." Submitted for publication, 1985. 15. Jones, R. L., "Central California Studies on the Degradation and Movement of Aldicarb Residues," July, 1985 (to be submitted for publication). 16. Porter, K. S., A. T. Lemley, Η. B. Hughes, R. L. Jones, "Developing Information on Aldicarb Levels in Long Island Groundwater," paper presented at the Second International Conference on Groundwater Quality Research, Tulsa, March 26-29, 1984. 17. Supak, J. R., A. R. Swoboda, J. B. Dixon, Soil Sci. Soc. Am. J., 1978 42, 244-247. 18. Bromilow, R. Η., Ann. Appl. Biol. 1973, 75, 473-479. 19. Martin, J. Μ., "Long Island Deep Soil Boring for Aldicarb Residues," Suffolk County Department of Health, 1981. 20. Jones, R. L., P.S.C. Rao, A. G. Hornsby, "Fate of Aldicarb in Florida Citrus Soil: 2. Model Evaluation," paper presented at Characterization and Monitoring of the Vadose (Unsaturated) Zone, Las Vegas, December 8-10, 1983. 21. Carsel, R. F., C. N. Smith, L. A. Mulkey, J. D. Dean, P. Jowise, "Users Manual for the Pesticide Root Zone Model (PRZM) Release 1", ΕΡΑ-60013-84-109, December 1984. 22. Carsel, R. F., L. A. Mulkey, M. N. Lorber, L. B. Baskin, "The Pesticide Root Zone Model (PRZM): A Procedure for Evaluating Pesticide Leaching Threats to Groundwater," accepted for publication, Ecological Modeling 1985. 23. Jones, R. L., "Movement and Degradation of Aldicarb Residues in Soil and Groundwater," presented at the Environmental Toxicology and Chemistry Conference on Multidisciplinary Aproaches to Environmental Problems, Crystal City, VA. 1983. 24. Lorber, Μ. Ν., "A Method for the Assessment of Groundwater Contamination Potential Utilizing PRZM - A Pesticide Root Zone Model for the Unsaturated Zone, presented at the ACS Symposium on Evaluation of Pesticides in Groundwater, Miami, April, 1985. 25. Wang, H. F., Μ. P. Anderson, "Introduction to Groundwater Modeling," W. H. Freeman, San Francisco, 1982. 26. Union Carbide, unpublished Florida unsaturated and saturated zone monitoring data, 1983 - 1985. RECEIVED April 1, 1986

Field, Laboratory, and Modeling Studies on the Degradation and

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